1. Field of the Invention
The present invention relates to a photomask material for manufacturing a semiconductor device.
2. Description of the Prior Art
A photographic emulsion plate employing a glass substrate has been utilized as a photomask material for manufacturing a semiconductor device. However, with the demand for high integration, i.e., micropatterning, a hard mask is now widely used which comprises a metal film, such as chromium (Cr), formed on a transparent glass substrate. Japanese Patent Laying-Open Gazette No. 157247/1982 discloses a photomask prepared by forming a silicon film and a metal film on a glass substrate and depicting a pattern on the films by electron beams (EB) to form a silicide pattern.
FIG. 1 is a schematic cross-sectional view of a conventional photomask material in which a metal film 2 of chromium or the like is formed on a transparent glass substrate 1 of silica or the like. Metal film 2 is formed on the transparent glass substrate 1 by evaporation or sputtering to a thickness of about 600 to 800 .ANG.. A photomask for manufacturing a semiconductor device is formed by coating a photoresist or an EB resist on the metal film 2 to depict a prescribed pattern on the resist film by actinic light or electron beams to be subjected to later processes such as development and etching. When the metal film 2 is made of chromium, such etching is performed by antimony cerium nitrate and perchloric acid in a wet process while the same is performed by a mixed gas of tetrachloromethane (CC1.sub.4) and oxygen (O.sub.2) in a dry process. The dry etching process has little side etching effect and is advantageous for manufacturing a semiconductor device such as VLSI involving high integration, i.e., micropattern.
Although the wet etching process is generally employed for manufacturing a conventional Cr photomask, it is difficult to form a highly precise mask due to the side etching effect. In the dry etching process, the etching rate of the Cr film is less than about 100 .ANG./min while selectivity of etching between the Cr film and the resist film is not so good, and hence the Cr photomask is not suitable for mass production. Further, the Cr film is inferior in adhesion to the quartz substrate, whereby the micropattern is apt to peel off when the mask is cleaned by ultrasonic method or scrubbing.